1. Field of the Invention
The present invention is related to a television apparatus which displays an image corresponding to a television signal.
2. Related Background Art
In the conventional television apparatus, above all, in the projection type television device using the projection tube, high luminance can be usually obtained by raising the anode voltage or beam current to the projection tube. However, in the case of the method to increase the anode voltage of the projection tube, there is a limitation in increasing the anode voltage, as X-ray generation amount is increased, and the pressure resistance of the glass at the projection tube, withstand voltage of inner electrode, etc. must be considered. In the case of electron beam amount increasing method by raising the beam current in the projection tube, where a single electron gun is used, the electron beam spot is enlarged at the high luminance time and, accordingly, the high precision degree is lowered, and such high prevision television signals as-EDTV, HDTV, etc. can not be reproduced sufficiently.
In this connection, as shown in the Japanese Laid-Open Patent Application No. 62-245792, an interference film filter is placed in front of red and green projection tube and such a blue projection tube is used, where 2 electron guns are provided, and the said blue projection tube is supplied with a television signal which is not delayed and also with a television signal which is delayed by one horizontal scanning period, so that the respective electron guns may be driven. In this way, the above problems found in the prior art are solved. However, since these electron guns are so arranged as to drive the television signal delayed by 1H (1 horizontal scanning period), it is necessary to make the afterglow time of a fluorescent body of blue projection tube to be shorter than 30 .mu.s, in the case of high precision television signals like EDTV or HDTV.
On the other hand, the afterglow time of blue fluorescent substances (Zn: Ag.Al) for such a projection tube as is aimed, as explained above, to have high luminance, is as long as 65 .mu.s (refer to FIG. 1A). This afterglow time is more than double in comparison with 1 horizontal scanning period (i.e., 30 .mu.s) of such high precision television signal as EDTV or HDTV.
The electron beam, supplied from the first electron gun to be driven by the television signal which is delayed by 1H, carries out the re-scanning, which the fluorescent body is still brightened by the scanning with the first electron gun and not yet sufficiently subdued. Hence, it cannot be so much expected that the luminance may be raised through the double scanning by the electron beam generated by 2 electron gun. (Refer to FIG. 1B)